Steelmaking slags as raw material for sulphoaluminate belite cement

Abstract: The present work was undertaken as part of the research in the Minerals and Metals Recycling research centre, MiMeR. The course of the thesis is attributed to metallurgical slags from the steelmaking industry and the possible use of such by-products as raw material for sulphoaluminate belite cement (SAB). Implementing steel slags into the production of cement could contribute to the steel industry's possibility of increasing the recirculation. In addition to the previous objective, the introduction of slag into the cement manufacturing can also facilitate the reduction of carbon dioxide emissions as well as lowering the overall energy consumption during the manufacturing. The reason for this is that the SAB system enables the reduction of the lime saturation factor (LSF) which in turn implies that less limestone is needed in the raw meal. Additionally, the firing temperature can be reduced by about 100-150°C, since dicalcium silicate and sulphoaluminate are formed already at approximately 1200-1250°C. In any event, one should remember that this is not intended to be a final solution for the recycling of slag, nor a replacement for already accepted cement materials. A number of applications currently exist where ordinary Portland cement (OPC) is used, but in cases where the OPC could be replaced with other type of cements, e.g. SAB cement, the possibility of using residues material in cement applications is increased. Considering the clinker covered within this work, possible applications are those where slow hydraulic properties are suitable. The behaviour of high temperature reactions of tested mixtures was investigated using thermogravimetric analysis coupled with a quadrupole mass spectrometer. Mineralogical observations were carried out with x-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results proved that steelmaking slags have the potential to work as raw material, since sulphoaluminate along with polymorphs of dicalcium silicate and ferrite phases were detected after firing at 1200 ºC in an air atmosphere. The hydraulic properties of the specimens were analysed through conduction calorimetry, XRD, differential scanning calorimetry (DSC) as was the mechanical strength of the specimens when hydrated for 2 and 28 days. The compressive strength was in accordance with that suggested in the literature for slow hardening SAB cement. Both mixtures tested behaved the same with regard to heat development as well as the amount of AFt formed during the first 24 hours of the hydration.